1. Field of the Invention
The present invention relates to a bearing device for various machines having a shaft member which relatively rotates in a cylindrical bearing through an oil film of lubricant, and more particularly, to a bearing device capable of preventing damage, wear, excessive heating and seizure of the device.
2. Description of the Prior Art
Conventionally, a bearing device which rotatably supports a shaft member in a bearing is widely used for various connected portion in construction equipment, earthmoving equipment, general equipment of hydraulic machine and the like. In the bearing device of this kind, lubricant for preventing internal wear is filled in sliding surfaces between a rotation shaft and a bearing which supports the rotation shaft. As the rotation shaft rotates, the lubricant is introduced into the sliding surfaces between the rotation shaft and the bearing to form a thin oil film. In this bearing device, when the rotation shaft is stopped or actuated or when fluctuating load is applied from outside, for example, the oil film is partially broken in some cases. If the oil film is partially broken or there is shortage of oil film, there are problems that a contact pressure between the rotation shaft and the bearing is increased, and friction heat caused by the contact pressure generates seizure between the rotation shaft and the bearing.
Japanese Patent Application Laid-open No. 9-68217, for example, discloses a bearing device which makes it possible to prevent the seizure of the bearing or the rotation shaft. According to this bearing device disclosed in this publication, a sliding surface of either one of a bearing and a rotation shaft is provided with a large number of machined surface portions having asperities of substantially trapezoidal cross sections along an axial direction or a rotation direction of the rotation shaft. The machined surface portions are formed at distances of several tens μm to several hundreds μm at intervals.
In the bearing device having the machined surface portions along the axial direction of the rotation shaft at intervals, a ratio of a mean upper base length to a mean lower base length of the substantially trapezoidal shapes of the machined surface portions is set to 0.6 or more and less than 1.0. In the bearing device having the machined surface portions in the rotation direction of the rotation shaft at intervals, a ratio of the mean upper base length to the lower base length of the substantially trapezoidal shapes of the machined surface portions is set to more than 0 and 0.6 or less.
With such shapes of the machined surface portions of the bearing device, oil film holding function of the lubricant is enhanced, and the oil film can be generated stably. Therefore, there is merit that the friction heat between the rotation shaft and the bearing is reduced, and the seizure in the rotation shaft or the bearing can be suppressed.
Generally, in a bearing device in which a rotation shaft and a bearing relatively slide on each other through an oil film of lubricant which is circulated and supplied to between the rotation shaft and the bearing, if a large number of oil-supply auxiliary groove portions for circulating and supplying the lubricant supplied from the oil-supply groove portion are provided on sliding surfaces between the rotation shaft and the bearing in addition to a main oil-supply groove portion which is directly connected to a lubricant supply source, a circulation and supply amount of the lubricant can be increased. However, if the number of oil-supply auxiliary groove portions is increased, although the seizure between the rotation shaft and the bearing is reduced, lengths in the rotation direction of land portions (sliding surfaces between the rotation shaft and the bearing) between the large number of oil-supply auxiliary groove portions are shortened, and an area of the sliding surfaces between the rotation shaft and the bearing is reduced. As a result, the contact pressure between the rotation shaft and the bearing is increased, and seizure is prone to be generated between the rotation shaft and the bearing by the friction heat caused by the contact pressure.
In order to overcome such inconvenience, a diameter of the rotation shaft and an inner diameter of the mating bearing are set greater and axial lengths of both the rotation shaft and the bearing are also increased so as to increase an area of the sliding surfaces between the rotation shaft and the bearing without changing the size of the oil-supply groove portion. That is, if the length of the land portion between the oil-supply auxiliary groove portions in the rotation direction and the axial direction is set longer, the area of the sliding surface between the rotation shaft and the bearing can be increased, and the contact pressure can be dispersed. However, if the diameter of the rotation shaft and the inner diameter of the mating bearing are set greater and the axial length is also set greater, there is a defect that the bearing device is naturally increased in size.
When the bearing device disclosed in the Japanese Patent Application Laid-open No. 9-68217 is used in a general apparatus in which a bearing and a rotation shaft continuously rotate relatively in one direction at high speed and under a high load, new lubricant is circulated and supplied to each sliding surface between the rotation shaft and the bearing through a recess of the machined surface portion, and the lubricant is prone to cause an adhesion state in which the entire surfaces of the rotation shaft and the bearing are coated.
On the other hand, in a bearing device mounted on a connection part of a utility machine of construction equipment or earthmoving equipment in which a rotation shaft and a bearing reciprocate and rotate through a predetermined angle at low speed and under a high load, relative sliding speed between an outer peripheral surface of the rotation shaft and an inner peripheral surface of the bearing is extremely slow, and the rotation shaft reciprocates and rotates through a same angle region a plurality of times in accordance with rocking motion of the utility machine. As a result, a large load is always applied in the contact angle region, the lubricant which is circulated and supplied to between the rotation shaft and the bearing is not prone to adhere to the entire surfaces of the rotation shaft and the bearing, and cut of oil film in which the oil film is partially broken or the shortage of oil film is prone to be generated.
When the bearing device disclosed in the above publication is used to the connection part of the utility machine of the construction equipment or the earthmoving equipment, even if sufficient lubricant can be circulated and supplied by the large number of oil-supply auxiliary groove portions, if the area of the sliding surfaces between the rotation shaft and the bearing is small, the contact pressure in the sliding surfaces between the rotation shaft and the bearing becomes extremely high. Therefore, in the bearing device of the connection part of the utility machine, it becomes difficult to obtain sufficient lubricating effect between the outer peripheral surface of the rotation shaft and the inner peripheral surface of the bearing.
As a result, abrasion, wear, excessive heat and the like are prone to be generated in the rotation shaft and the bearing due to the partial oil film break and the shortage of oil film, and the seizure is prone to be generated in the rotation shaft and the bearing due to the friction heat caused by the contact pressure. Further, if the oil film is broken or the like, vibration or noise is generated and thus, the performance of the construction equipment or the earthmoving equipment may be seriously deteriorated. Therefore, the bearing device disclosed in the above publication cannot exhibit the satisfactory lubricating effect with respect to the sliding surfaces between the rotation shaft and the bearing in the bearing device used under conditions of low speed, low rocking angle and high load such as the utility machine above.
In the bearing device disclosed in the publication, the oil film is stably generated by forming the large number of machined surface portions having specific shape along the axial direction or the rotation direction of the rotation shaft, and it is expected to suppress the seizure of the rotation shaft and the bearing. That is, as in the low speed rocking and high load bearing device mounted on the connection part for the utility machine in the construction equipment or the earthmoving equipment mentioned above, a bearing device in which a utility machine is rocked in the entire region from a determined small rocking region to a determined large rocking region and sliding motion having large contact pressure between the rotation shaft and the bearing is carried out, even if the above bearing device is employed, it is extremely difficult to reduce the sliding resistance as well as the seizure of the rotation shaft and the bearing because of its structure.
The bearing device for low speed rocking and high load cannot secure wear resistance and seizure resistance only by changing the shape of the machined surface portions, and it is not possible to solve the conventional technical problems that the shortage or break of oil film is generated, and seizure is prone to be generated in the rotation shaft and the bearing.